Today, there is a drive to replace more of the electrical interconnections in computer and networking systems with optical interconnections in order to increase computation speed and communication bandwidth. These systems typically comprise a plurality of daughterboards that are interconnected to one another by a common optical backplane. Each daughterboard has a plurality of electrical pins or tabs disposed at one of its edges, which mate with corresponding electrical receptacles on the common optical backplane. The optical connections are generally accomplished by an optical ribbon connector that runs between the daughterboard and the optical backplane. One end of the optical ribbon connector is typically anchored to the daughterboard, while the other end has an optical connector that interlocks with an optical receptacle that is anchored to the optical backplane. Light is transmitted into the optical fibers by one or more arrays of vertical-cavity surface-emitting laser (VCSEL) diodes located on respective daughterboards, and light is received from the optical fibers by one or more arrays of conventional photodetectors located on respective daughterboards. The optical fibers are typically multimode fibers (i.e., fibers that transport light having multiple spatial modes).
One problem with the optical ribbon connector method has been the loss of light at the connection. The loss generally occurs when the light traverses the gap between the optical fiber of the ribbon and a corresponding optical fiber of the receptacle. The light exits the end of the optical fiber going in a plurality of different directions, and some of the light is not collected into the end of the opposing optical fiber because the gap does not have a waveguiding structure. Light is also lost because of misalignment between the ends of the optical fibers. One solution to this problem has been to place a prefabricated microlens adjacent to each fiber end in the receptacle to better collect the light emitted from the ribbon fiber, and to focus it on the fiber end in the receptacle. These microlenses also focus light exiting the receptacle fiber so that the light does not stray as it passes through the gap. Alternatively, these microlenses have been placed at the ends of the ribbon fibers. Both of these approaches, however, suffer from misalignment problems, which result in loss of light. In addition, both of these approaches require expensive and time-consuming micro-alignment procedures to place the microlenses in their optimal locations.
Accordingly, efficient coupling of light from ribbon optical fibers to the receptacle optical fibers has not been fully achieved.